Green house effect and global warming are more or less the same. The contrast however is that, the green house effect explains the idea of global warming but green houses dont contribute to global warming. Global warming occurs when harmful gases are released to the atmosphere, they then cause a barrier, a blanket like cover in the atmosphere which prevents sufficient heat loss from the ground. this increased heat that can not escape to the atmosphere because of the layer of gases then leads to global warming. this is the same principle through which a green house operates.